Straight man discovered aboard ship (6)
I believe the answer is:
linear
'straight' is the definition.
(I've seen this before)
'man discovered aboard ship' is the wordplay.
I cannot really see how this works, but
'man' could be 'lin' and 'lin' is found within the answer.
The remaining letters 'ear' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for linear that I've seen before include "In one dimension, I learn (anag.)" , "Of a line or length" , "adopting common narrative style" , "Straight; sequential" , "Consisting of lines" .)